For example, a rotating electrical machine such as a generator includes a stator having an armature winding, a rotor having a field winding, and a brush. The brush is provided in pressure contact to a slip ring in a slidable manner, the slip ring being provided to the end of the field winding. The brush supplies an excitation current from a battery to the field winding.
When the brush has worn to interrupt energization between the brush and the slip ring, electric power supply from the battery to the field winding is stopped, and the rotating electrical machine fails to operate. In this case, the replacement of the brush is essential for restarting the rotating electrical machine.
If the rotating electrical machine fails to operate when a device mounting the rotating electrical machine is in operation, the device itself may break down. Particularly in the case where the rotating electrical machine is mounted in a vehicle, if the brush has worn to stop the operation of the rotating electrical machine, the vehicle may be seriously damaged.
Accordingly, in order to prevent an abnormal operation stop of the rotating electrical machine due to the wear of the brush, the life of the brush derived in consideration of a brush wear amount corresponding to an expected operating time of the rotating electrical machine is set to be sufficiently longer than a guaranteed performance period of the rotating electrical machine.
In order to lengthen the life of the brush, however, it is necessary to increase the length of the brush. The increased length of the brush results in increased size of the rotating electrical machine and increased cost.
In view of the above-mentioned problem, there have been proposed various types of rotating electrical machines including a device for warning of the arrival of replacement timing of the brush by estimating a wear amount of the brush.
A conventional brush wear detector for a vehicle generator includes a current detection circuit for detecting a current value flowing to the field winding of the generator via the brush of the generator, an output voltage detection circuit for detecting an output voltage value of the generator, and a brush wear determination circuit for determining a wear state of the brush based on the current value detected by the current detection circuit or the output voltage value detected by the output voltage detection circuit (see, for example, Patent Literature 1).
The brush includes a pair of a brush (+) and a brush (−). Each of the pair of brushes is urged and pressed against a slip ring by a coil spring.
The conventional brush wear detector for a vehicle generator detects an initial excitation current that flows through the field winding at the start of rotation of an engine, and determines the wear state of the brush based on the initial excitation current.
The conventional brush wear detector for a vehicle generator can warn that the brush has reached a wear limit based on the result of determination of the brush wear determination circuit. Thus, the brush can be replaced before energization between the brush and the slip ring is interrupted, to thereby avoid an abnormal operation stop of the conventional vehicle generator due to the wear of the brush.
A conventional brush monitoring device for a rotating electrical machine includes current-corresponding wear amount calculation means for obtaining a brush wear amount corresponding to an armature current detection value or a physical detection value correlated to an armature current based on current-wear amount characteristics, and rotational speed-corresponding wear amount calculation means for obtaining a brush wear amount corresponding to an armature rotational speed detection value or a physical detection amount correlated to an armature rotational speed based on rotational speed-wear amount characteristics. A warning is issued when a cumulative wear amount obtained by cumulatively adding the brush wear amounts calculated by those calculation means has exceeded a wear limit (see, for example, Patent Literature 2).
In the conventional brush monitoring device for a rotating electrical machine, a warning is issued when the cumulative wear amount has exceeded a wear limit. Thus, the brush can be replaced before energization between the brush and the slip ring is interrupted, to thereby avoid an abnormal operation stop of the conventional rotating electrical machine due to the wear of the brush.
A conventional brush wear management device for a servo motor includes an activation count counter for counting an activation count of a servomotor equipped with a brush, and an operating time counter for counting operating time of the servo motor equipped with a brush. The wear amount of the brush is calculated in consideration of not only one of the activation count counter and the operating time counter but also the other, and a warning is issued when it is determined that the brush has reached the end of the life based on the calculated wear amount of the brush (for example, Patent Literature 3).
In the conventional brush wear management device for a servo motor, a warning is issued when it is determined that the brush has reached the end of the life. Thus, the brush can be replaced before energization between the brush and the slip ring is interrupted, to thereby avoid an abnormal operation stop of the conventional servo motor due to the wear of the brush.